Ovulation is the phase of a female’s menstrual cycle in which a mature egg is released from the ovarian follicles into the oviduct. It refers to the rupture of the ripened follicle in the ovary to discharge the egg ready for fertilization at middle of the menstrual cycle. After ovulation, during the luteal phase, the egg will be available to be fertilized by sperm. Concomitantly, the lining of the uterus (the endometrium) is thickened to be able to receive a fertilized egg. If no conception occurs, the uterine lining as well as blood will be shed during menstruation.

An ovum can survive for about 12 hours after it leaves the ovary. It can get fertilised only if it comes into contact with a sperm within this time frame. Sperms, however, can live in the female genital tract for 48 hours or even 72 hours.

The menstrual cycle, under the control of the endocrine system, is necessary for reproduction. It is commonly divided into three phases: the follicular phase, ovulation, and the luteal phase. Menstrual cycles are counted from the first day of the present menstrual bleeding to the first day of the next menstrual bleeding. Hormonal contraception interferes with the normal hormonal changes with the aim of preventing reproduction. The duration of menstrual cycle varies from person to person and is usually between 26 to 31 days. Ovulation occurs approximately in the middle of the cycle, i.e. duration of the cycle - (minus) 14 days.

A week before and a week after the approximate day of ovulation is considered fertile period. The days apart from this are called the safe periods, where the fertilization does not take place.

Safe period

Every month a woman is in safe period that means if you mate with a woman during that time then the chances of her getting pregnant is almost nil. The chances are almost nil because one has to be very careful calculating the safe period. Any miss calculation will result in fertilization.

You have to note your period for at least 6 months and note the number of days between starting date and the next period to know your safe period. Then identify longest and shortest period cycles.

Calculation of Safe Period

The calendar method is most reliable if a woman has a regular period cycle. It is also based on the assumption that ovulation in most ladies takes place at about fourteenth day before the next menstrual flow. The implication of the above is that in a regular period cycle, it can be assumed that ovulation will take place on the fourteenth day before the next period.

If for example, a women’s menstrual cycle varies from 26 days to 31 days cycle.

The shortest cycle [26days] minus 18days = 8th day.

The longest cycle [31days] minus 10days = 21st day.

8th to 21st day of each cycle counting from first day of menstrual period is considered as fertile period. Period other than this fertile period in a menstrual cycle is considered as safe period.

How safe is safe period?

The calendar method for family planning is almost cost-free. All that is required is the calendar and two pens – a red and blue pen. The red pen is used to mark the ovulation day and the preceding ‘unsafe’ six days and the next four days are also underlined in red. The blue pen is used to underline the other days as the ‘safe days’.

The major shortcoming is that the calendar method could be quite tricky, since the pattern of fertility can suddenly change appreciably in the same person over time. Like some ladies would have realized that sometime ago their cycles might have hovered around 28 days and later came down to say 24 days or more – that is stretching to say 33 days. This is common and may be normal.

Safe period is not 100% reliable and so caution should be taken.

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